1. Field of the Invention
The present invention relates to a filter device for decontaminating a contaminated fluid in which chips, fine sludge, etc., are mixed, for example.
2. Description of the Related Art
A machine tool or the like for machining, such as cutting, grinding, etc., uses a fluid such as a coolant for cooling a workpiece. This fluid is mixed with foreign matter, such as chips produced by machining, fine sludge, etc. In order to reuse the contaminated fluid that contains the chips, sludge, etc., a filter device is used to remove the chips, sludge, etc., from the contaminated fluid.
The inventors hereof have long been investigating and developing filter devices and developed, as part of them, a filter device that uses a filter element formed of a punching metal. For example, a punching-metal filter element is described in Jpn. UM Appln. KOKOKU Publication No. 4-33929. In manufacturing the punching metal, a large number of punch holes are bored through a metal plate by means of a press die that has a large number of pins. These punch holes are formed at predetermined pitches in the metal plate. This punching metal is formed into a cylindrical shape and set in a filter tank. As a contaminated fluid flows from the outer peripheral side of the filter element to the inner peripheral side, chips and the like that are contained in the contaminated fluid adhere to the punch holes.
The punch holes of the punching-metal filter element are formed by means of the press die that has the large number of pins. The punch holes that are punched out by the pins of the die have an inner surface that is straight in the thickness direction of the metal plate. The inner surface of the punch holes is rugged, having shear marks and the like. Inevitably, moreover, openings of the punch holes are subject to projections such as burrs. In this filter element, chips are liable to stick in or be caught by the punch holes, so that the chips cannot be disengaged with ease. In some cases, therefore, the chips may fail to be removed by only rubbing the surfaces of the filter element with a scraper blade, so that clogging may occur.
In order to form the punch holes in the metal plate with use of the die that is provided with the large number of pins, moreover, a relatively soft material must be used as the metal plate for the punching metal. Therefore, the punching-metal filter element has low stiffness and is easily deformable. Depending on the contact state of the scraper blade for removing the chips adhering to the filter element, the punching metal may be deformed, thus leaving room for improvement.